Understanding chmod: A Beginner’s Guide to File Permissions in Linux

 In Linux and other Unix-like operating systems, every file and directory has a set of permissions that control who can read, write, or execute the file. These permissions are essential for ensuring that only authorized users and processes can access files and directories. In this article, we’ll introduce the chmod command and explain how to use it to change file permissions in Linux.

Understanding File Permissions in Linux In Linux, file permissions are divided into three sets: one for the user who owns the file (the owner), one for the members of the file’s group, and one for everyone else. Each set of permissions can be represented by a combination of three letters: r for read, w for write, and x for execute. For example, rwx means that the user has permission to read, write, and execute the file.

Using the chmod Command The chmod command is used to change the permissions of a file or directory. It can be used with either letters or numbers to represent the permissions. For example, to give the owner of a file full permissions (read, write, and execute), but only allow the group and others to read the file, you could use either of these commands:

chmod u+rwx,g+r,o+r myfile

chmod 744 myfile

Both commands do the same thing: they give the owner (u) read (r), write (w), and execute (x) permissions; they give the group (g) read (r) permission; and they give others (o) read (r) permission.

1. Understanding Numerical Permissions In addition to using letters to represent permissions, chmod can also use numbers. Each set of permissions (user, group, and other) can be represented by a number from 0 to 7. The number is calculated by adding the values for each permission that is granted: 4 for read (r), 2 for write (w), and 1 for execute (x). For example, 7 means full permissions (rwx), because 4 + 2 + 1 = 7.

In this article, we’ve introduced the basics of file permissions in Linux and explained how to use the chmod command to change them. With this knowledge, you’ll be able to manage access to your files and directories more effectively.